A phenomenon where light is emitted by a force applied to a material is called mechanoluminescence (ML). To date, the mechanoluminescent principle is not clearly defined and is being merely researched for scholarly interest.
Examples of the ML include emission of X-ray, which is caused by delamination of a scotch tape in a vacuum state, and emission of ultraviolet (UV) ray caused by an ultrasound wave. The ML has a fundamental problem where light is emitted due to friction or breakdown, and for this reason, is very low in industrial application possibility.
The Xu group of national institute of advanced industrial science and technology (AIST) attempted to solve a problem, where the ML is low in industrial application possibility, by applying non-destructive ML called deformation luminescence where light is emitted by elastic or plastic deformation of a material, instead of triboluminescence and fractoluminescence caused by friction or breakdown, to a stress sensor.
However, in an application attempted by the Xu group of AIST, since a general UV-curable polymer is used as a stress transfer material that transfers a mechanical force to a luminescent material for luminescence, it is difficult to transfer a repetitive stress, and consequently, a lifetime of an application product is short.
Moreover, brightness, lifetime (or reproducibility), and color control are very important factors for actually applying the ML to various industries, but there is no research on brightness, lifetime, and color control.
In order to solve such a problem, the applicant has disclosed a stress transfer material with enhanced brightness and lifetime (a mechanoluminescent composite film and a method of manufacturing the same disclosed in Korean Patent Application No. 10-2013-0042869) and has disclosed technology for controlling a luminescence spectrum based on a composite film having characteristics such as high brightness and long lifetime (a mechanoluminescent composite film for controlling color and a color control method thereof disclosed in Korean Patent Application No. 10-2013-0042870, PCT/KR2013/007545). Also, the applicant has disclosed an environment-friendly display driven by wind (a mechanoluminescent display device disclosed in Korean Patent Application No. 10-2014-0070171, PCT/KR2014/012089).
The applicant has realized ML based on a mixture where zinc sulphide (ZnS, a mechanoluminescent material) is mixed with polydimethylsiloxane (PDMS, a stress transfer material), and the mixture corresponds to a structure for realizing electroluminescence (EL). That is, in a case of using an elastic material, ML and EL are simultaneously realized.
Moreover, the mixture enables simultaneous observation of a color expression effect based on electro deformation and a color expression effect based on mechanical deformation, based on a feature where a color realized based on EL differs from a color realized based on ML, and moreover, a hybrid display based on a new concept is implemented.
However, to date, research is not sufficiently done on a luminescent material which expresses different colors by independently controlling electro-deformation and mechanical deformation to be applied to the hybrid display based on the new concept.